This invention relates to the field of ink jet printing systems, and more specifically to a printhead support assembly and ink supply arrangement for a printhead assembly and such printhead assemblies for ink jet printing systems.
Micro-electromechanical systems (xe2x80x9cMEMSxe2x80x9d), fabricated using standard VLSI semi-conductor chip fabrication techniques, are becoming increasingly popular as new applications are developed. Such devices are becoming widely used for sensing (for example accelerometers for automotive airbags), inkjet printing, micro-fluidics, and other applications. The use of semi-conductor fabrication techniques allows MEMS to be interfaced very readily with microelectronics. A broad survey of the field and of prior art in relation thereto is provided in an article entitled xe2x80x9cThe Broad Sweep of Integrated Micro-Systemsxe2x80x9d, by S. Tom Picraux and Paul McWhorter, in IEEE Spectrum, December 1998, pp24-33.
In PCT Application No. PCT/AU98/00550, the entire contents of which is incorporated herein by reference, an inkjet printing device has been described which utilizes MEMS processing techniques in the construction of a thermal-bend-actuator-type device for the ejection of a fluid, such as an ink, from a nozzle chamber. Such ink ejector devices will be referred to hereinafter as MEMJETs. The technology described in the reference is intended as an alternative to existing technologies for inkjet printing, such as Thermal Ink Jet (TIJ) or xe2x80x9cBubble Jetxe2x80x9d technology developed mainly by the manufacturers Canon and Hewlett Packard, and Piezoelectric Ink Jet (PIJ) devices, as used for example by the manufacturers Epson and Tektronix.
While TIJ and PIJ technologies have been developed to very high levels of performance since their introduction, MEMJET technology is able to offer significant advantages over these technologies. Potential advantages include higher speeds of operation and the ability to provide higher resolution than obtainable with other technologies. Similarly, MEMJET Technology provides the ability to manufacture monolithic printhead devices incorporating a large number of nozzles and of such size as to span all or a large part of a page (or other print surface), so that pagewidth printing can be achieved without any need to mechanically traverse a small printhead across the width of a page, as in typical existing inkjet printers.
It has been found difficult to manufacture a long TIJ printhead for full-pagewidth printing. This is mainly because of the high power consumption of TIJ devices and the problem associated therewith of providing an adequate power supply for the printhead. Similarly, waste heat removal from the printhead to prevent boiling of the ink provides a challenge to the layout of such printhead. Also, differential thermal expansion over the length of a long TIJ-printhead may lead to severe nozzle alignment difficulties.
Different problems have been found to attend the manufacture of long PIJ printheads for large- or full-page-width printing. These include acoustic crosstalk between nozzles due to similar time scales of drop ejection and reflection of acoustic pulses within the printhead. Further, silicon is not a piezoelectric material, and is very difficult to integrate with CMOS chips, so that separate external connections are required for every nozzle.
Accordingly, manufacturing costs are very high compared to technologies such as MEMJET in which a monolithic device may be fabricated using established techniques, yet incorporate very large numbers of individual nozzles. Reference should be made to the aforementioned PCT application for detailed information on the manufacture of MEMJET inkjet printhead chips; individual MEMJET printhead chips will here be referred to simply as printhead segments. A printhead assembly will usually incorporate a number of such printhead segments.
While MEMJET technology has the advantage of allowing the cost effective manufacture of long monolithic printheads, it has nevertheless been found desirable to use a number of individual printhead segments (CMOS chips) placed substantially end-to-end where large widths of printing are to be provided. This is because chip production yields decrease substantially as chip lengths increase, so that costs increase. Of course, some printing applications, such as plan printing and other commercial printing, require printing widths that are beyond the maximum length that is practical for successful printhead chip manufacture.
The present invention is broadly directed to the provision of a suitable printhead segment support structure and ink supply arrangement for an inkjet printhead assembly capable of single-pass, full-page-width printing as well as to such printhead assemblies. While the invention was conceived in the context of MEMJET printhead segments (chips), and thus the following summary and description of the invention is provided with particular reference to printhead assemblies incorporating MEMJET printhead segments, it is believed that the invention also has the potential to be employed with other ink jet printhead technologies.
Accordingly, it is one object of the present invention to provide a printhead segment support structure that is capable of accommodating a series of printhead segments as described in PCT/AU98/00550 in an array that permits single-pass pagewidth printing across the width of a surface passing under the printhead assembly.
The term xe2x80x9csingle-pass pagewidth printingxe2x80x9d should here be understood as referring to a printing operation during which the printhead assembly is moved in only one direction along or across the entire width or length of any print surface, as compared to a superimposed, generally orthogonal printhead carriage movement as employed in conventional ink jet printers. (Of course, printhead assembly movement may be relative, with the surface moving past a stationary printhead assembly.) It will be also understood that there are many possible page widths and the inkjet printhead segment support structure of the invention would be suitable for adaptation to a range of widths. A printhead assembly in accordance with the invention should in particular be useful where a plurality of generally elongate, but relatively small printhead segments are to be used to print across substantially the entire width of a sizable surface without the need for mechanically moving the printhead assembly or any printhead segment across as well as along the print surface.
The invention has also been conceived in light of potential problems related to the relatively small size of individual printhead segments, their fragility and the required highly accurate alignment or registration of individual printhead segments with each other on the support structure and with external components in order to provide a printhead assembly capable of single-pass, full pagewidth printing. Multiple ink supply channels are required to supply ink in reliable manner to all printhead segments. Because of the small size of the segments, this in general would require high quality micro-machined parts. An ink supply conduit, on the other hand, is most economically made if it can be formed at a much coarser scale.
Accordingly, another object of the invention is to provide a printhead segment support structure with a print fluid supply arrangement that ensures adequate print fluid (eg ink) supply to individual printhead segments mounted to the support structure, at an affordable manufacturing cost.
Typical MEMJET printhead segments have a dimension of 2 cm length by 0.5 mm width, and will include (in a layout for 4-color printing) four lengthwise-oriented rows of ink ejection nozzles, the segment being of monolithic fabrication. Longer segments could be made and used, but the size mentioned gives very satisfactory fabrication yields. Each printhead segment has ink inlet holes arrayed on one surface and corresponding nozzle outlets arrayed on an opposite surface. Each of the four rows will then require connection to an appropriate ink supply, such that an inkjet printhead assembly can be provided for operation with (for example) cyan, magenta, yellow and black inks for color printing.
Accordingly, yet a further object is to provide an ink supply arrangement thereby to enable supply of a number of differently colored inks (or other printing fluids) to selected ink inlets of individual printhead segments carried on a support structure for full pagewidth color printing.
Another related object of the invention is to provide a print fluid supply arrangement that is simple in layout and thus easy to incorporate in a printhead support structure. It should ensure even and reliable distribution of print fluids in a pagewidth inkjet printhead assembly.
In a first aspect, the invention provides a support for a plurality of inkjet printhead segments, said support including:
a hollow elongate member having at least one ink supply channel formed therein, the, or each, ink supply channel being in fluid communication with an elongate slot in and extending at least partly along the elongate member; and
a plurality of printhead segment carriers received and secured in neighbouring arrangement within the slot, each printhead segment carrier being adapted for mounting thereto of at least one printhead segment.
Each printhead segment carrier may include at least one ink gallery that is in fluid communication with said, or an associated one of said, ink supply channels when mounted to that printhead segment carrier.
The printhead segment carriers may be configured so that when the printhead segments are mounted in the printhead segment carriers they define a series of printing ranges in a direction lengthwise along the elongate member that overlap to define a combined printing range of greater lengthwise extent than any of the printing ranges of the respective printhead segments.
The printhead segment carriers may be substantially identical to one another and may have stepped terminal ends thereby to enable neighbouring pairs of printhead carriers to be mounted within the slot in a staggered manner.
Each printhead segment carrier may have an elongate recess in an external surface of the carrier within which at least one printhead segment is mountable and wherein recesses of neighbouring pairs of carriers overlap in a direction along the elongate member.
Each printhead segment carrier may define an elongate ink delivery slot that opens into said recess of each printhead segment carrier. Each ink delivery slot may be in fluid communication with a respective ink supply channel via said ink gallery that extends from said at least one ink slot to an opening in a rear face of the printhead segment carrier.
A plurality of said ink galleries and said openings may be in fluid communication with the, or each, ink delivery slot. Said openings associated with the, or each, said ink delivery slot may be arranged in a row extending in a direction along the elongate member.
Each printhead segment carrier may have a plurality of ink supply channels and a plurality of said rows of openings. Each row of openings may be aligned along its length with one said ink channel for passage of ink from said ink channel through said row of openings.
The ink galleries may be defined by a plurality of parallel walls extending transversely in each printhead segment carrier and intersecting with a plurality of converging walls extending from the rear face to shaped inner edges that at least partially define the ink delivery slots.
The assembly may include a shim that is shaped to be received in the slot in the elongate member and to lie between the elongate member and said printhead segment carriers, said shim having at least one aperture therein to permit flow of ink between the or an associated one of said ink supply channels and a corresponding one ink gallery of the respective printhead segment carrier.
The shim and the slot may be substantially semi-circular in cross-sectional shape.
The shim and/or the elongate member may comprise means for snap-fittingly mounting said shim at said slot. In another example, the shim may be adhesively bonded to mating surfaces of the elongate member. In yet another example, the printhead segment carriers may be adhesively bonded to the shim.
Webs, which abut external surfaces of the elongate member, may be attached to edges extending in a direction along the shim.
Each printhead segment carrier may have a recess formed in an external surface thereof within which at least one printhead segment is received when mounted to the printhead segment carrier. Said external surface may have a second recess formed therein and adapted to receive at least a part of a power or signal conductor terminating on the or one said printhead segment mounted to the printhead segment carrier.
Said conductor may comprise a tape automated bonded (TAB) film.
Said tape automated bonded film (TAB) may be wrapped around an external surface of the elongate member and terminated on a printed circuit board secured to a side of the elongate member opposite to the printhead segment to which it is connected.
The support assembly may include a first cap secured to a first terminal end of the elongate member and may have an ink inlet port in fluid communication with the or an associated one of said ink supply channels.
The support assembly may further include a second cap secured to a second terminal end of the elongate member and having an opening for bleeding of air from the or an associated one of said ink supply channels. Means for sealing off said opening after such bleeding may be provided.
Said second cap may include an outer face with a tortuous channel formed therein. Said tortuous channel may be in fluid communication with said opening and said sealing means may include a film removable at least in part from the outer face and adapted to adhere to the outer face thereby to cover the tortuous channel and seal off the opening.
The support assembly may further include an external protective shield plate covering the printhead segment carriers and having openings arranged to permit unimpeded passage of ink ejected from nozzles of printhead segments mounted to the carriers towards a surface passing beneath the support assembly.
The elongate member may have three, four or six of said ink supply channels, one each for a differently colored ink.
Each printhead segment carrier may be mounted within the slot at a longitudinal position within a predetermined distance of a designated longitudinal position of the carrier corresponding to a designated longitudinal position within the slot of a printhead segment when mounted to said printhead segment carrier.
The elongate member may be of substantially constant cross-sectional shape along its entire length.
In cross-section, the elongate member may include a peripheral structured wall including a base wall section, and side wall sections standing out from opposite edges of said base wall section, and wherein said slot lies between free edges of said side wall sections.
Said elongate member may further include at least one internal web extending from the base wall section and along said elongate member.
Said elongate member may have a plurality of said internal webs. In cross-section, said free edges of the side wall sections and free edges of said internal webs may lie on a semicircle and may define boundaries of said slot so that said slot is of semicircular cross-section.
In a second aspect, the invention provides an inkjet printhead assembly including:
a hollow elongate member having at least one ink supply channel formed therein, the or each ink supply channel being in fluid communication with an elongate slot in and extending at least partly along the elongate member; and
a plurality of printhead segment carriers received and secured in neighbouring arrangement within the slot; and
at least one printhead segment mounted to each printhead segment carrier.
Thus, the second aspect of the invention is directed to a printhead assembly that includes the support assembly of the first aspect of the invention.
It is preferred that the at least one printhead segment on each printhead segment carrier has a defined printing range in a direction lengthwise along the elongate member, and that the printing ranges of the printhead segments mounted to a plurality of adjoining printhead segment carriers overlap, so that the printhead segments mounted to said plurality of adjoining printhead segment carriers have a combined printing range of greater lengthwise extent than any of the printing ranges comprised therein. This is a suitable way in which printing may be accomplished on a surface without the presence of gaps corresponding to lengthwise gaps between individual printhead segments.
In a further aspect, the invention provides a method for assembling the inkjet printhead assembly wherein the step of mounting to each printhead segment carrier its respective at least one printhead segment precedes the step of securing that printhead segment carrier within the slot. It is then preferred that the printhead segment carriers are secured within the slot sequentially, and that the at least one printhead segment in each printhead segment carrier installed after the first is positioned longitudinally relative to the at least one printhead segment in the printhead segment carrier last installed before being finally secured and immobilized within the slot. Thus, accurate relative positioning of successive printhead segments lengthwise along the elongate member can be achieved.
Other aspects, objects and advantages of the invention, in its different embodiments, will also become apparent from the description given below of preferred embodiments and from the appended claims.